Halogenated flame-retardants are widely used in polymer compositions to impart flame-retardant properties. However, halogenated flame-retardants, and particularly those containing aliphatic halogen, are susceptible to deterioration or degradation during processing in an organic polymer or upon subsequent thermal aging of the polymer composition. Hydrohalide acids such as HCl or HBr, that are generated during the processing or aging history, can both autocatalytically degrade the halogen-containing flame retardant and catalytically degrade the organic polymer. The ensuing chain scission typically results in undesirable lowered melt viscosity and discoloration of the composition.
Many compounds and compositions have been used to stabilize halogen-containing organic polymers during processing, during subsequent aging, and during recycling. Examples include organotin mercaptides, sulfides, and carboxylates, mixed metal stabilizer systems such as barium/cadmium, barium/zinc, and calcium/zinc, lead-based stabilizers such as sulfates, stearates, carbonates, phthalates, and phosphites, and metal-free systems based on aminocrotonic acid esters. These are discussed in Plastics Additives Handbook edited by R. Gachter and H. Muller, Hanser Publishers, 3rd Edition, pp. 281-300, hereby incorporated by reference.
Costabilizers are also used. They do not possess a thermo-stabilizing effect, but improve the effectiveness of one or more primary stabilizers. Examples include organic phosphites, epoxy compounds, polyols, phenolic antioxidants, 1,3-diketones, dihydropyridine, and betaketocarboxylic acid esters. These are discussed at pages 300-308 of the Plastics Additives Handbook referenced above, hereby incorporated by reference.
The prior art discloses the use of these stabilizers and costabilizers in single-stabilizer and multi-stabilizer systems. For example, U.S. Pat. Nos. 4,089,912, 4,183,846, 4,217,258, 4,219,605, 4,532,287, 4,558,083, 4,593,059, and 4,963,606, hereby incorporated by reference, disclose various systems containing dibutyltin maleate or other organotin compounds. U.S. Pat. Nos. 4,154,718, 4,299,759, 4,427,816, 5,106,898, 5,141,980, 5,216,058, and 5,234,981, hereby incorporated by reference, disclose systems incorporating hydrotalcite and similar stabilizer compounds.
Although these stabilizers have been known for many years, an improved solution to stabilizing flame-retarded polyolefin and polystyrene compositions is needed. Compounders prefer working at higher temperatures in order to increase their throughput, and the increased emphasis on recycling requires working with feed streams containing a variety of additives. Both scenarios require a robust stabilizer system to protect the polymer composition.